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Re: Miscompilation of remainder expressions

From: Roberto Bagnara <bagnara at cs dot unipr dot it>
To: Robert Dewar <dewar at adacore dot com>
Cc: gcc at gcc dot gnu dot org
Date: Tue, 16 Jan 2007 19:11:33 +0100
Subject: Re: Miscompilation of remainder expressions
References: <45AB8770.5040402@cs.unipr.it> <45AD0BD4.9090809@adacore.com>

Robert Dewar wrote:

Roberto Bagnara wrote:

Reading the thread "Autoconf manual's coverage of signed integer
overflow & portability" I was horrified to discover about GCC's
miscompilation of the remainder expression that causes INT_MIN % -1
to cause a SIGFPE on CPUs of the i386 family.  Are there plans to
fix this bug (which, to me, looks quite serious)?


Seems ultra-non-serious to me, hard to believe this case appears
in real code, despite surprising claim by Roberto.


How do you test if a number is a multiple of another one?
What about rounding toward zero to a multiple of k?
I guess

x - x%k

looks like unreal code to you.

--
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara@cs.unipr.it

References:
- Miscompilation of remainder expressions
  - From: Roberto Bagnara
- Re: Miscompilation of remainder expressions
  - From: Robert Dewar

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